Method of selecting the cellular system with which a cellular mobile radiotelephone communicates

Abstract

A remotely programmable cellular mobile radiotelephone (CMR 12) is configured to select (1300) a cellular system (14-16) with which to communicate while roaming. The CMR (12) utilizes a default system selection process. The system selected using this default process is identified (1302) and a SID list (1402) is checked to see if the system identification number (SID) of the identified system is on the list (1402). The SID list (1402) is maintained in a current state through remote programming sessions (1500). When the default system's SID is not on the list (1402), CMR (12) operation continues normally. When the default system's SID is on the SID list (1402), the default system selection process is replaced with an alternate system selection process (1316-1322). If a new system selected by the alternate process is not available or if a new system is available but listed on the SID list (1402), then the CMR (12) simulates a no service mode of operation (1332-1338). Simulation of a no service mode of operation ceases when an actual no service condition occurs (1222). If a new system selected by the alternate selection process is available and not listed on the SID list (1338), then operation on the new system is permitted. After a predetermined duration of operation on the new system, the default selection process is restored and the procedure repeats if necessary.

What is claimed is: 
     
       1. A method of selecting upon which one of a plurality of frequency sets a cellular mobile radiotelephone (CMR) communicates, said method comprising the steps of: storing a list of system identification numbers (SIDs) that identify cellular base systems for which cellular radiotelephone communication with said CMR is to be prohibited;   detecting when said CMR is roaming;   when said CMR is roaming, obtaining a SID for the cellular system upon which said CMR is currently configured to operate, said cellular system communicating upon a first one of said sets of frequencies;   determining whether said SID is identified by said list; and   when said SID is identified by said list, instructing said CMR to communicate upon a second one of said sets of frequencies.   
     
     
       2. A method as claimed in claim 1 additionally comprising the steps of: periodically receiving revision data, said data being received at said CMR over one of said plurality of sets of frequencies; and   storing said data in said list of SIDs, said receiving and storing steps operating to maintain said list in a current state.   
     
     
       3. A method as claimed in claim 1 wherein: prior to said detecting step, said CMR operates in an original system selection mode;   said instructing step causes said CMR to operate in an altered system selection mode; and   when said SID is not identified by said list, said method comprises the step of continuing operation of said CMR in said original system selection mode.   
     
     
       4. A method as claimed in claim 1 wherein, when communication services are unavailable, said CMR operates in an unavailability mode of operation which prevents transmissions away from said CMR, and said method additionally comprises, when said SID is identified by said list, the steps of: determining whether communication services are available over said second frequency set;   when said communication services are unavailable, instructing said CMR to communicate upon said first frequency set; and   operating said CMR in a mode of operation that simulates said unavailability mode.   
     
     
       5. A method as claimed in claim 4 additionally comprising, the steps of: monitoring operation of said CMR upon said first frequency set to determine when communication services become actually unavailable; and   terminating said simulation of said unavailability mode when said communication services become actually unavailable.   
     
     
       6. A method as claimed in claim 4 wherein said operating step comprises the step of permitting said CMR to place emergency calls in spite of said simulation of said unavailability mode. 
     
     
       7. A method as claimed in claim 1 wherein, when communication services are actually unavailable, said CMR operates in an unavailability mode of operation which prevents transmissions away from said CMR, and said method additionally comprises, when said SID is identified by said list, the steps of: determining whether communication services are available over said second frequency set;   when said communication services are available, obtaining a SID for a second cellular system which communicates using said second frequency set;   determining whether said second system SID is identified by said list; and   when said second system SID is identified by said list, simulating CMR operation in said unavailability mode.   
     
     
       8. A method as claimed in claim 7 wherein said obtaining a SID for said second cellular system step is performed only when said CMR is roaming with respect to said second cellular system. 
     
     
       9. A method as claimed in claim 7 additionally comprising, when said second system SID is identified by said list, the steps of: monitoring operation of said CMR to determine when communication services become actually unavailable; and   terminating said simulation of said unavailability mode when said communication services become actually unavailable.   
     
     
       10. A method as claimed in claim 9 additionally comprising, when said second system SID is identified by said list, the step of instructing said CMR to communicate upon said first set of frequencies. 
     
     
       11. A method as claimed in claim 1 wherein said method additionally comprises, when said SID is identified by said list, the steps of: determining whether communication services are available over said second frequency set;   when said communication services are available, getting a SID for a second cellular system which communicates using said second frequency set;   inquiring whether said second system SID is identified by said list; and   when said second system SID is not identified by said list, waiting a predetermined period of time then instructing said CMR to communicate upon said first set of frequencies; and   repeating said obtaining, and determining steps.   
     
     
       12. A method of preventing a cellular mobile radiotelephone (CMR) that is capable of performing a plurality of cellular system selection processes from operating upon a predetermined set of cellular systems, said method comprising the steps of: periodically receiving data at said CMR, said data identifying at least one cellular system;   storing said data in a list within a memory portion of said CMR;   performing a first one of said cellular system selection processes to select a first cellular system upon which said CMR may operate;   obtaining a system identification number (SID) of said first cellular system;   comparing said SID against said list to determine whether said CMR is prevented from operating upon said first cellular system; and   when said comparing step determines that said CMR is prevented from operating upon said first cellular system, performing a second one of said cellular system selection processes.   
     
     
       13. A method as claimed in claim 12 additionally comprising the steps of: detecting when said CMR is roaming with respect to said cellular system selected in accordance with said first process; and   omitting said comparing step when said CMR is not roaming.   
     
     
       14. A method as claimed in claim 12 wherein: when one of said selection processes fails to detect a cellular system with which said CMR may communicate, said CMR operates in an unavailability mode of operation; and   said method additionally comprises, when said comparing step determines that said CMR is prevented from operating upon said first cellular system, the steps of: determining whether said second one of said processes detects a second cellular system with which said CMR may communicate;   when said second cellular system is not detected, performing said first process; and   operating said CMR in a mode of operation that simulates said unavailability mode.     
     
     
       15. A method as claimed in claim 14 wherein said operating step comprises the step of permitting said CMR to place emergency calls in spite of said simulation of said unavailability mode. 
     
     
       16. A method as claimed in claim 14 additionally comprising the steps of: monitoring the performance of said first process to determine when said first process fails to detect a cellular system with which said CMR may communicate; and   terminating said simulation of said unavailability mode when said first process fails to detect a cellular system with which said CMR may communicate.   
     
     
       17. A method as claimed in claim 12 wherein: when one of said selection processes fails to detect a cellular system with which said CMR can communicate, said CMR operates in an unavailability mode of operation; and   said method additionally comprises, when said comparing step determines that said CMR is prevented from operating upon said first cellular system, the steps of: determining whether said second one of said processes detects a second cellular system with which said CMR can communicate;   when said second cellular system is detected, obtaining a system identification number (SID) of said second cellular system;   comparing said second system SID against said list to determine whether said CMR is prevented from operating upon said second cellular system; and   when said second system comparing step determines that said CMR is prevented from operating upon said second cellular system, simulating CMR operation in said unavailability mode.     
     
     
       18. A method as claimed in claim 17 wherein said comparing said second system SID step is performed only when said CMR is roaming with respect to said second cellular system. 
     
     
       19. A method as claimed in claim 17 additionally comprising, when said second system comparing step determines that said CMR is prevented from operating upon said second cellular system, the steps of: monitoring the performance of one of said first and second processes to determine when said one process fails to detect a cellular system with which said CMR can communicate; and   terminating said simulation of said unavailability mode when said one process fails to detect a cellular system with which said CMR can communicate.   
     
     
       20. A method as claimed in claim 12 wherein said method additionally comprises, when said comparing step determines that said CMR is prevented from operating upon said first cellular system, the steps of: determining whether said second one of said processes detects a second cellular system with which said CMR can communicate;   when said second cellular system is detected, obtaining a SID of said second cellular system;   inquiring whether said second system SID identifies a cellular system upon which said CMR is prevented from operating;   when said CMR is not prevented from operating upon said second cellular system, waiting a predetermined period of time then performing said first cellular system selection process; and   repeating said obtaining, and comparing steps.   
     
     
       21. A method of selecting upon which one of a plurality of frequency sets a cellular mobile radiotelephone (CMR) communicates, said method comprising the steps of: periodically receiving data, said data being received at said CMR over one of said plurality of sets of frequencies;   storing said data in a list of system identification numbers (SIDs) that identify cellular systems for which cellular radiotelephone communication with said CMR is to be prohibited, said receiving and storing steps operating to maintain said list in a current state;   detecting when said CMR is roaming;   when said CMR is roaming, obtaining a SID for the cellular system upon which said CMR is currently configured to operate, said cellular system communicating upon a first one of said sets of frequencies;   determining whether said SID is identified by said list;   when said SID is identified by said list, instructing said CMR to communicate upon a second one of said sets of frequencies;   determining whether communication services are available over said second frequency set;   when said communication services are available, getting a SID for a second cellular system which communicates using said second frequency set;   inquiring whether said second system SID is identified by said list;   when said second system SID is not identified by said list, waiting a predetermined period of time, then instructing said CMR to communicate upon said first set of frequencies; and   repeating said obtaining, and determining steps.   
     
     
       22. A method as claimed in claim 21 wherein, when communication services are unavailable, said CMR operates in an unavailability mode of operation which prevents transmissions away from said CMR, and said method additionally comprises: when said communication services are unavailable over said second set of frequencies, instructing said CMR to communicate upon said first frequency set; and   operating said CMR in a mode of operation that simulates said unavailability mode.